DE112016003002T5 - Stabilized quantum dot structure and method for producing a stabilized quantum dot structure - Google Patents

Abstract

A stabilized quantum dot structure for use in a light emitting diode (LED) according to one embodiment comprises a luminescent particle comprising one or more semiconductors, a buffer layer over the luminescent particle, the buffer layer comprising an amorphous material, and a barrier layer over the buffer layer Barrier layer contains oxygen, nitrogen and / or carbon. In another embodiment, the stabilized quantum dot structure comprises a luminescent particle comprising one or more semiconductors and a treated buffer layer comprising amorphous silica over the luminescent particle, wherein the stabilized quantum dot structure has a quantum efficiency of at least about 0.7, if one Exposed to blue light flux of about 30 W / cm 2 at a temperature of 80 to 85 ° C and a relative humidity of 5% for 500 hours.

Description

Related Application

The present invention claims priority under 35 U.S.C. §119 (e) of U.S. provisional application filed on Jun. 30, 2015. Patent Application No. 62 / 186,698, which is incorporated herein by reference in its entirety.

Technical area

The present invention relates generally to light emitting devices, and more particularly to stabilized quantum dot structures for lighting and display applications.

background

Luminescent quantum dots are promising as adjustable narrowband down-light converters to complement and replace conventional phosphors. A down-converting quantum dot or phosphor can absorb light of a particular wavelength (e.g., blue) and emit light at a longer wavelength (e.g., red). One of the main limitations of quantum dots as buck converters for lighting and display applications is their instability under high luminous flux conditions and / or elevated temperature conditions, especially in the presence of ambient oxygen and moisture. The stress of such oxidative and hydrolytic conditions can lead to progressive decomposition of the quantum dot structure, deterioration of the down-conversion efficiency, and spectral changes in the down-converted light.

Brief summary of the invention

A stabilized quantum dot structure having excellent stability during use in a light-emitting device has been developed.

In one embodiment, a stabilized quantum dot structure comprises a luminescent particle comprising one or more semiconductors, a buffer layer over the luminescent particle, the buffer layer comprising an amorphous material, and a barrier layer over the buffer layer, wherein the barrier layer is oxygen, nitrogen and / or carbon includes.

In another embodiment, the stabilized quantum dot structure comprises a luminescent particle comprising one or more semiconductors and a buffer layer over the luminescent particle, the buffer layer comprising an amorphous material and an additional chemical species for stabilizing the quantum dot structure.

In another embodiment, the stabilized quantum dot structure comprises a luminescent particle comprising one or more semiconductors and a treated buffer layer comprising amorphous silica overlying the luminescent particle, the stabilized quantum dot structure having a quantum efficiency of at least about 0.7. when exposed to a blue light flux of 30 W / cm ² at a temperature of 80 to 85 ° C and a relative humidity of 5% for 500 hours.

A method for producing a stabilized quantum dot structure comprises: forming a luminescent particle comprising one or more semiconductors; Forming a buffer layer comprising an amorphous material on the luminescent particle thereby to form a coated luminescent particle; and forming a barrier layer comprising oxygen, nitrogen and / or carbon on the coated luminescent particle to enhance its stability, thereby forming a stabilized quantum dot structure.

A method for producing a stabilized quantum dot structure comprises: forming a luminescent particle comprising one or more semiconductors; Forming a buffer layer comprising an amorphous material on the luminescent particle thereby to form a coated luminescent particle; and treating the coated luminescent particle to improve its stability and form a stabilized quantum dot structure, wherein the stabilized quantum dot structure has a quantum efficiency of at least about 0.7 when exposed to a blue light flux of 30 W / cm ² at a temperature of 80 to 85 ° C and a relative humidity of 5% for 500 hours.

The terms "comprising,""including,""containing," and "having" are used interchangeably in the present specification as non-terminological terms to refer to the mentioned elements (or steps) without the non-mentioned elements (or steps ) exclude.

Brief description of the drawings

1 shows a schematic representation of a first embodiment of the stabilized quantum dot structure.

2 shows a schematic representation of a second embodiment of the stabilized quantum dot structure.

3 shows a schematic representation of a third embodiment of the stabilized quantum dot structure.

4 shows a schematic representation of an exemplary core-shell structure of a luminescent particle, in which example the luminescent particle comprises a semiconductor core, which is surrounded by a first semiconductor shell and a second semiconductor shell.

5A and 5B show a quantum efficiency (QY) and a deviation from a peak of QY-stabilized luminescent particles (the upper data), which has a buffer layer comprising untreated silica and a barrier layer comprising zinc oxide (CdSe / CdS / SiOx / ZnO), coated, compared with luminescent particles (the lower data), which have no zinc oxide barrier layer on the untreated silicon dioxide buffer layer (CdSe / CdS / SiOx).

5C FIG. 12 shows a peak position shift as a function of time for the stabilized luminescent particles (the above data) coated with a buffer layer comprising treated silica and a barrier layer comprising Al ₂ O ₃ compared to the luminescent particles (FIG. lower data) which do not have an Al ₂ O ₃ barrier layer on the treated silicon dioxide buffer layer.

6A to 6B show the quantum yield of the stabilized luminescent particles coated with a treated layer comprising amorphous silica and an ionic species (K) due to pH treatment, it being understood that over time improved stability for higher pH treatments is achieved. Value, with initial pH levels peaking in the range of 11.8 to 2.0.

7A FIG. 12 shows an exemplary light-emitting device having an LED chip in optical communication with the stabilized quantum dot structure of any embodiment of the present invention.

7B - 7D show exemplary housing arrangements for a light emitting device having an LED chip and a plurality of stabilized quantum dot structures.

8A - 8E show exemplary lighting fixtures using the light emitting devices and the stabilized quantum dot structures described herein.

9A Figure 4 shows a quantum yield as a function of time (from t = 0 to 504 hours) for the treated coated luminescent particles that were subjected to a pre-bake process prior to packaging in a package and operation in an LED component.

9B Figure 12 shows the quantum yield as a function of time (from t = 0 to 504 hours) for the treated coated luminescent particles that were pre-baked before being placed in a package and operated in an LED component.

10 Figure 4 shows Fourier transform infrared spectroscopy (FTIR) curves obtained from the silica-coated luminescent particles before and after annealing.

11 shows a quantum yield as a function of time (hours) for the coated luminescent particles (CdSe / CdS / SiOx) with and without annealing.

12 shows mass loss data for the coated luminescent particles (CdSe / CdS / SiOx) as a result of annealing.

13A and 13C show TEM images of untreated (non-annealed) coated luminescent particles, and 13B and 13D show TEM images of treated coated luminescent particles (after annealing).

14 Fig. 12 is a graph of particle size distribution before and after annealing determined by analyzing TEM images.

15 Figure 4 shows an energy dispersive X-ray spectroscopy (EDX) spectrum for a stabilized quantum dot structure which has been pH treated after formation of the buffer layer.

16A and 16B show quantum dot structures before and after the formation of a zinc oxide barrier by a solution phase coating process.

17A - 17C Figure 4 shows TEM images of stabilized quantum dot structures comprising CdSe / CdS / SiOx / Al ₂ O ₃ wherein the Al ₂ O ₃ barrier layer is formed by a vapor deposition process (atomic layer deposition (ALD)).

18A - 18C Figure 4 shows TEM images of stabilized quantum dot structures comprising CdSe / CdS / SiOx / ZnO where the ZnO barrier layer is produced by ALD.

19A - 19C show TEM images of quantum dot structures comprising a mixture of CdSe / CdS / ZnS and SiOx / Al ₂ O ₃ wherein the Al ₂ O ₃ barrier layer is formed by ALD.

20A - 20C Figure 4 shows TEM images of stabilized quantum dot structures comprising CdSe / CdS / ZnS / SiOx / ZnO where the ZnO barrier layer is produced by ALD.

Detailed description

definitions

A first device, described as being "in optical communication with" a second device, is arranged such that light from the first device reaches the second device or vice versa.

A "dominant wavelength" refers to a wavelength of light that has the same visible color as the light emitted by an LED, as perceived by the human eye. The dominant wavelength differs from the peak wavelength in that the dominant wavelength accounts for the sensitivity of the human eye to different wavelengths of light.

A quantum dot structure may be described using a slash notation (eg, "x / y / z"), where x is a kernel or layer below y, which is a layer below z. In other words, z is a layer that partially or completely overlies or surrounds y, which in turn is a layer that partially or completely overlaps x.

It should be understood that when an element such as a layer, region or substrate is described as being "on top" of another element, it may be disposed directly on top of the other element or intervening elements may also be present , Further, relative terms such as "inner," "outer," "upper," "above," "over," "overlying," "below," "below," "above," "below," and the like may be used herein used to describe a relationship between elements. It should be understood that these terms are intended to encompass orientations of the device that differ from those shown in the figures.

Although the terms first, second, etc. may be used herein to describe various elements, components, regions, layers and / or sections, they should not be limited by these terms. These terms are used only to distinguish one element, component, region, layer or section from another section, layer or section. Thus, a first element described below, first Component, first region, first layer or first portion, may be referred to as a second element, second component, second region, second layer or second portion without departing from the teachings of the present invention.

The figures are merely schematic illustrations. Therefore, the actual dimensions and shapes of the devices and components (eg, layer thicknesses) may be different, and deviations from the representations may occur as a result of, for example, manufacturing processes and / or tolerances. Embodiments should not be construed to be limited to the particular shapes of the ranges illustrated herein, but are intended to encompass variations in shapes that arise, for example, in manufacturing. An area shown or described as a square or rectangle may have rounded or curved structures due to normal manufacturing tolerances. Thus, the areas shown in the figures are purely schematic in nature and their shapes are not intended to represent the exact form of a portion of a device, and to limit the scope of the invention.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used herein, the singular forms "a," "an," and "the," are also intended to include plurals, unless the context clearly indicates otherwise. It is also to be understood that the terms "comprising," "comprising," "containing," and / or "including" indicate the presence of indicated features, integers, steps, operations, elements, and / or components, but not the presence, or Exclude one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

Unless otherwise defined, all terms (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It is further understood that the terms used herein are to be interpreted as having a meaning consistent with their meaning in the context of this specification and the relevant prior art, and are not to be interpreted in an idealized or overly formal sense unless expressly defined herein.

Described herein are various embodiments of a stabilized quantum dot structure having improved reliability under high luminous flux conditions and / or elevated temperature conditions. The stabilized quantum dot structure can withstand degradation generated by ambient oxygen and ambient humidity during a long operating life (eg,> 10,000 hours).

Referring to 1 includes the stabilized quantum dot structure 100 a luminescent particle 102 comprising one or more semiconductors. A buffer layer 104 comprising an amorphous material overlies the luminescent particle 102 , and a barrier layer 106 , which has oxygen, nitrogen and / or carbon, lies above the buffer layer 104 , The oxygen, nitrogen and / or carbon can be understood as part of a chemical compound, and therefore it can be said that the barrier layer 106 an oxygen, nitrogen and / or carbon-containing compound. For example, the barrier layer 106 an oxide, a carbide, a nitride, an oxynitride, an oxycarbide or other compound. An amorphous or non-crystalline structure of the buffer layer 104 Can the continuous, reproducible growth of the barrier layer 106 facilitate, which serves as a barrier to gaseous oxygen and moisture. The buffer and barrier combination can prevent deterioration of the luminescent particle by limiting or eliminating environmental species that otherwise interact with and degrade the surface of the luminescent particle.

According to one embodiment, the buffer layer comprises 104 amorphous silica (SiO _x , where 0.5 ≦ x ≦ 2.5, for example, SiO ₂ ) and the barrier layer 106 includes an oxide that is different from silicon dioxide. Other suitable amorphous materials for the buffer layer 104 For example, amorphous titanium dioxide, amorphous carbon, amorphous alumina, amorphous silicon oxycarbide or amorphous aluminosilicate may be included. In some embodiments, the barrier layer 106 a stoichiometric or non-stoichiometric oxide, carbide or nitride compound. Exemplary oxides used for the barrier layer 106 include semiconductive oxides such as zinc oxide, titanium dioxide, indium oxide, tin oxide, nickel oxide and copper oxide, conductive oxides such as indium-tin oxide, aluminum-doped zinc oxide and gallium-doped zinc oxide, or insulating oxides such as alumina, zirconia or hafnium oxide. Suitable carbides include silicon carbide or boron carbide, and suitable nitrides include silicon nitride, gallium nitride, boron nitride or aluminum nitride.

The preparation of an oxide coating directly on the surface of the semiconductive luminescent particle was difficult or impossible, at least in part, due to the difference in lattice constants and / or crystal structures between the oxide and the semiconductor. This difference can lead to unfavorable deformation and / or surface energy conditions that can prevent the oxide from reproducibly coating the luminescent particles. Under ordinary liquid phase growth conditions, the inventors have observed that oxides tend to form discrete particles and / or a partial coating instead of a continuous coating on the semiconductor surface. It is believed that the presence of a buffer layer comprising an amorphous material provides a suitable interface for continuous growth of the oxide or other material, such as a carbide or nitride compound.

In 2 a further embodiment of the stabilized quantum dot structure is shown. As described above, the stabilized quantum dot structure includes 200 a luminescent particle 102 comprising one or more semiconductors; and a buffer layer 104 containing an amorphous material over the luminescent particle 102 includes. In this embodiment, the buffer layer is 104 after a stabilization treatment, a treated buffer layer (or "a treated layer") 108 comprising the amorphous material. For example, the treated buffer layer 108 the amorphous material and an additional chemical species. As another example, the treated buffer layer 108 an annealed or densified buffer layer, as described in more detail below.

For example, in the first example, the additional chemical species may be a dopant or an ion species such as K and / or Na. Such additional chemical species may be delivered to the buffer layer via a treatment process (eg, a pH treatment process) as described below. The presence of the additional chemical species can be confirmed by energy dispersive X-ray spectroscopy (EDX) and, in some cases, the method can be used to qualitatively determine the relative amount of additional chemical species in the buffer layer. For example, with reference to the EDX spectrum discussed in US Pat 15 2, the relative intensity of the additional chemical species (in this case K) is at least about 0.4, at least about 0.5, or at least about 0.6 as compared to a major line of one of the buffer layer components (Si or O in this case) , The treated buffer layer 108 In some cases, it may comprise a silicate salt such as potassium silicate or sodium silicate comprising the ionic species. Additionally or alternatively, the ionic species may be in the form of mobile ions in the amorphous material.

In the other example mentioned above, the treated buffer layer 108 be a tempered or densified buffer layer. In this case, due to the increased density of the buffer layer, environmental species such as water and oxygen can not penetrate the buffer layer quickly and the quantum dot structure can show improved stability during LED operation. The properties of the annealed and densified buffer layers are described in more detail below.

A luminescent particle 102 that of a treated buffer layer 108 which has an additional chemical species for stabilization and / or has been densified by annealing can be compared with a luminescent particle 102 containing only an untreated buffer layer 104 having improved stability (for example, when exposed to high flux at elevated temperatures and / or humid conditions). Accordingly, a barrier layer 106 on the treated layer 108 may not be required.

Alternatively, with regard to the stabilized quantum dot structure 300 of the 3 the treated layer 108 as described above as a buffer layer between the luminescent particle 102 and a barrier layer 106 , which has an oxygen, carbon and / or nitrogen-containing compound serve. In other words, the barrier layer 106 over the treated layer 108 lie. A quantum dot structure 300 containing both the treated layer 108 as well as the barrier layer 106 can exhibit exceptional stability when exposed to oxidative or hydrolytic conditions at elevated temperatures under high luminous flux. For example, this shows in 5C The diagram shows that an additional improvement in stability occurs when a barrier layer is deposited on a compacted (treated) buffer layer. When comparing the top curve to the bottom curve, the reduced shift in emission peak position as a function of time shows increased stability for the quantum dot structure, which is both a treated layer 108 as well as an overlying barrier layer 106 having.

As in 4 shown, the luminescent particle 102 In any previously described embodiment, a core-shell structure comprising a semiconductor core 102 with a first semiconductor and a first semiconductor layer 102b over the core 102 comprising a second semiconductor. The semiconductor core 102 can serve as a light emission center, and the first semiconductor shell 102b can act as an absorption enhancer. In one example, the first semiconductor may comprise a Group II-VI semiconductor such as CdSe, and the second semiconductor may comprise CdS. The luminescent particle may further comprise a second semiconductor shell 102c over the first semiconductor shell 102b and comprise a third semiconductor. The second semiconductor shell 102c may serve as a high quality, substantially defect-free release layer and include, for example, ZnS in one example. The first, the second and / or the third semiconductor may each differ from each other and be monocrystalline or polycrystalline.

Restricting the particle size (or crystal size) of a semiconductor material to within a few to a few tens of nanometers (that is, near or less than the Bohr radius of an exciton) is called quantum confinement; electronic carriers within these so-called quantum dots are spatially limited. Discrete energy levels can occur, as opposed to the continuous bands of allowed energies in large volume semiconductors, and the bandgap energy is increased. The smaller the particle size - and the stronger the restriction - the greater the increase. Thus, the emission wavelength can be controlled by varying the quantum dot size (ie, the luminescent particle), with larger particle sizes associated with a red shift in emission. For applications on light emitting diodes, it is advantageous that the luminescent particle absorbs blue light and converts the blue light down to a longer emission wavelength (eg, green, yellow, or red). As previously mentioned, the first shell 102b act as an absorption enhancer and are thus designed to absorb blue light during the semiconductor core 102 serves as a light emission center and can be optimized for down conversion to a particular wavelength (for example, red). Typically, the semiconductor core 102 have a size of about 1.5 nm to about 5 nm, and the first semiconductor shell 102b may have a thickness of about 0.5 nm to about 20 nm. If present, the second semiconductor shell 102c have a thickness of about 0.5 nm to about 20 nm. The luminescent particle 102 has a linear size (for example, width or diameter) of less than 100 nm, and typically the linear size is less than 50 nm or less than 20 nm. Due to the size at the nanoscale, the luminescent particle 102 also referred to as a luminescent nanoparticle.

Alternatively, the luminescent particle must 102 have no core-shell structure, and may instead comprise a (single) semiconductor material or illuminant material. The semiconductor or phosphor material may be a down converter of blue or UV light wavelengths and may further be single crystal or polycrystalline.

The untreated or treated buffer layer 104 . 108 and / or the barrier layer 106 can be essentially transparent to visible light. Typically, the barrier layer has 106 an average thickness of about 2 nm to about 50 nm. Similarly, the buffer layer comprising the amorphous material may have an average thickness of about 2 nm to about 50 nm. In some cases, the buffer layer and / or barrier layer have a greater thickness of up to about 1 micrometer, or up to about 500 nm (eg, from about 2 nm to about 500 nm, or from about 2 nm to about 100 nm). Advantageously, both the buffer layer and the barrier layer are a continuous layer that completely surrounds the underlying layer. In some cases, however, both the buffer layer and the barrier layer may be sub-layers that do not completely surround the underlying layer. In the case of the buffer layer, the underlying layer is the luminescent particle, and in the case of the barrier layer, the underlying layer is the buffer layer.

The improved stability of the stabilized quantum dot structure - which may include one or more coatings or layers on a luminescent particle as described above - can be demonstrated by comparing the quantum efficiency of stabilized and non-stabilized quantum dot structures as a function of time. 5A and 5B show the quantum yield (QY) and a deviation from the peak QY as a function of time for (lower trace) non-stabilized quantum dot structures comprising CdSe / CdS / SiO _x where the SiO _{x is} untreated and (upper trace) for stabilized quantum dot structures having a zinc oxide (ZnO) barrier over the CdSe / CdS / (untreated) SiO _x structure. As previously mentioned, shows 5C the increased stability that can be achieved when a barrier layer is deposited on a treated buffer layer (eg, a buffer layer that has been subjected to an annealing treatment, such as 500 ° C for 5 minutes in nitrogen). The upper curve of the 5C is of a stabilized quantum dot structure with a barrier layer on the treated buffer layer, and the lower curve is of a quantum dot structure with no barrier layer on the treated buffer layer. Specifically, the data were obtained from the CdSe / CdS / (treated) SiO _x structures with and without an Al ₂ O ₃ barrier layer.

In a similar way shows 6A the quantum yield as a function of time for stabilized quantum dots having a treated buffer layer; In this example, the treated layer is amorphous silica which has been subjected to pH treatment with potassium hydroxide. Initial pH values were in a peak range of 11.8 to 2.0 (11.8, 11.0, 9.0, 5.5, 2.0). The treated layer thus comprises an additional ion species (K) which can be detected by EDX. For coated luminescent particles which are subjected to pH treatment with an initial pH in the range of 10.0 to 12.0, an improvement in stability is observed, with an initial pH of about 11.0 to 12.0 being preferred becomes. In the examples of both 5A as well as 6A For example, the quantum dot structure exhibits a quantum efficiency of at least about 0.7 after being exposed to a blue light flux of 30 W / cm ² at a temperature of 80 to 85 ° C and a relative humidity of 5% for 500 hours. After being exposed to a blue light flux of 30 W / cm ² at a temperature of 80 to 85 ° C and a relative humidity of 85% for 500 hours, as in the example of 6B the quantum yield is at least about 0.6.

The quantum efficiency (QY) can be determined by the spectral output of an LED measured in a calibrated Ulbricht sphere. The quantum yield is the ratio of the sum of the down converted photons to the number of absorbed blue photons (or source photons). In one method, the number of blue absorbed photons (source photons) is determined by measuring a (blue) LED without down-converting material (QDs) and then by adding a down-converting material and remeasuring the spectra and forming the difference determined from the blue photons without quantum dots and the blue photons with down-converting material. That is, QY = red photons / [(blue photons without QDs) - (blue photons with QDs)].

The quantum dot structure according to any embodiment of the present invention may be used as a light-emitting device. For example, with reference to the schematic view of 7A the light-emitting device 720 a blue light emitting diode (LED) chip 730 comprising a dominant wavelength of 425 nm to about 475 nm, which is in optical communication with multiple quantum dot structures 700 for down converting the emitted light. In this example, the quantum dot structures are 700 on a surface of the blue LED chip 730 applied. The blue LED chip 730 can on a submount (substrate) 740 be arranged, and a lens or sheath 750 can over the LED chip 730 although other submount or package configurations are possible, as described in more detail below. Instead of a plot of the quantum dot structures 700 directly on the blue LED chip 730 These may alternatively be on an outer or inner surface of the lens 750 be applied. Similarly, the quantum dot structures 700 over the entire volume of the sheath 750 be arranged. There may be more than one type of LED chip (blue and / or other colors) as well as additional phosphors and / or quantum dot structures in the light-emitting device 720 be used.

The light-emitting device having the stabilized quantum dot structures described herein may have any number of different package configurations. As is well known in the art, to use an LED chip in circuitry or the like, an LED chip may be enclosed in a package to protect it from environmental and / or mechanical influences, and color selection, light focusing, and the like sure. An LED housing also includes electrical leads, contacts or traces for electrically connecting the LED housing to an external circuit.

A typical LED housing 10 is in 7B shown. In this example is a single LED chip 12 on a reflective shell 13 attached by means of a solder joint or a conductive epoxy resin. One or more wire connections 11 connect the contacts of the LED chip 12 with the wires 15A and or 15B attached to the reflective shell 13 fastened or integrally formed with this. The reflective shell may be coated with a sheath material 16 be filled, which may contain a wavelength conversion material, such as a phosphor and / or the quantum dot structures. The entire assembly is then covered with a protective resin 14 sheathed, which may be shaped in the shape of a lens to that of the LED chip 12 to collect emitted light.

Another conventional LED housing 20 is in 7C and includes one or more LED chips 22 mounted on a carrier, such as a printed circuit board (PCB) carrier, as well as leads and a substrate or submount. According to this embodiment, a reflector surrounds 24 who is on a submount 23 is mounted, the LED chip or the LED chips 22 and reflects that from the LED chip (s) 22 emitted light from the housing 20 path. The reflector 24 offers the LED chips 22 also mechanical protection. There may be one or more wire bonds 27 between the contacts on the LED chips 22 and the electric tracks 25A . 25B on the submount 23 getting produced. The mounted LED chips 22 then be with a sheath 26 such as a silicone, to protect the chips from environmental and mechanical influences while also acting as a lens. As previously described, the sheath may comprise one or more wavelength conversion materials, such as the stabilized quantum dot structures described herein. Other exemplary LEDs include LED packages formed of a plastic material molded around a lead frame and the one or more LED chips mounted in a cavity of the housing and an optically transmissive jacket such as silicone , is distributed in the cavity over the one or more LED chip / s. Again, one or more wavelength conversion materials, such as the stabilized quantum dot structures, may be distributed throughout the cladding.

Another exemplary LED housing 30 is in 7D and includes an LED chip 34 on a submount 32 , wherein a molded lens 70 , such as a silicone lens, is formed over it. The Lens 70 may include one or more wavelength conversion materials, such as the stabilized quantum dot structures described herein, dispersed therein and / or on the LED chip. The LED chip 32 can also be coated with a conversion material that can convert all or most of the light from the LED. The lens may be formed in various shapes such as hemispherical, planar, separated or the like. An example of such LEDs is in the U.S. Patent Nos. 9,070,850 and 9,048,396 which are assigned to the same assignee as the present application and hereby incorporated by reference. It should be noted that in the U.S. Patent No. 9,070,850 other reference numerals than in 7D be used. Alternative embodiments of the light-emitting device including a plurality of LEDs mounted in a cavity and covered with a cladding material having wavelength-converting materials dispersed therein are disclosed in US Pat U.S. Patent No. 8,624,271 which is assigned to the same assignee as the present application and hereby incorporated by reference.

In general, the LED chips include one or more active layers of semiconductor material disposed between oppositely doped layers. When a bias voltage is applied to the doped layers, holes and electrons are introduced into the active layer where they recombine to produce light. The light is emitted from the active layer and from the different surfaces of the LEDs. The light is emitted at a primary wavelength through the LED chip. The primary radiation may be absorbed by the wavelength conversion material (eg, phosphor, stabilized quantum dot structure, etc.) that in response emits light at a secondary wavelength (s). The primary and / or secondary wavelengths of light may mix to obtain a desired light color. As one of ordinary skill in the art will appreciate, depending on the primary wavelength (s) and the fill level of the one or more wavelength conversion materials, as well as their light absorption / emission characteristics, different color temperatures of white light may be generated by the LEDs.

The schematic in 7A - 7D LED chips shown may be nitride-based Group III LED chips whose active region is formed of nitrogen and Group III elements such as aluminum, gallium and / or indium in the form of epitaxially grown and doped nitride layers as well for a person skilled in the art to produce light in the green to UV spectral range, for example blue light. As shown in the previous examples, multiple quantum dot structures may be incorporated in silicone or other optically transmissive cladding material and applied to the LED chip. In further embodiments, the quantum dot structures may be arranged in and / or on a jacket and / or optic of the LED chip, such as, for example, silicon, epoxy or glass. The quantum dot structures may be emitted at the same or different wavelengths depending on the composition and size of the luminescent particles. In addition, phosphors such as red nitride phosphors and / or green or yellow LuAG or YAG phosphors may be mixed with and / or separated (eg, in a remote phosphor configuration) on the optics and / or in discrete layers with the quantum dot structures in the matrix be arranged on the LED chip. The result may be a light emitting device that emits warm white light (eg, 2700 K to 4000 K) and / or has a high CRI (greater than 90) and / or has an increased color gamut.

The LED components, packages, and light emitting devices described above can be fabricated using methods known in the art, as described, for example, in U.S. Patent Application Publication No. 2012/0280261 entitled "Light Emitting Diode (US Pat. LED) for Achieving an Asymmetric Light Output ", which is hereby incorporated by reference. In addition, the blue LED chips may be coated with the aforementioned quantum dot structures or phosphors using any suitable method, such as that described in US Patent Application Publication Nos. 2008/0179611 and 2008/0173884, both entitled " Wafer Level Phosphor Coating Method and Devices Fabricated Utilizing Method "and hereby incorporated by reference. As described in these patent applications, LED chips may be coated and / or sprayed with phosphors, the stabilized quantum dot structures, and / or other wavelength conversion materials. The LED chips may also be formed using Electrophoretic Deposition (EPD), such as the EPD method described in U.S. Pat U.S. Patent No. 8,563,339 by Tarsa et al. entitled "Closed Loop Electrophoretic Deposition of Semiconductor Devices", which is hereby incorporated by reference.

The light emitting devices and stabilized quantum dot structures described herein are particularly useful with respect to various form factor lights. For example, each embodiment disclosed herein may alternatively be implemented with various types of solid state lights, including downlights, troffers, street lights, canopy lights, parking garage lights, lights using waveguide technology, and other lighting devices. 8A shows an omnidirectional bulb, such as an A19 bulb. Other similar consumer lights, such as PAR, BR and candelabra bulbs, may also implement the light-emitting devices described herein. Exemplary lights are in the U.S. Pat. Nos. 8,591,062 and 8,596,819 and in the U.S. Patent Publication No. 2015/0362168 described herein by reference. 8B shows another downlight that may use the light-emitting devices described herein. An example of such a downlight is in the U.S. Patent No. 8,777,449 which is incorporated herein by reference. 8C Figure 4 shows a Troffer luminaire which may use the light-emitting devices described herein. An exemplary Troffer luminaire is disclosed in published US patent publication no. US 2012/0327650 which is incorporated herein by reference. In another example shows 8D solid state street lighting that can use the light emitting devices described herein. Other streetlights and exterior lighting fixtures that may be implemented using the light-emitting devices described herein include the fixtures that are incorporated herein U.S. Patent No. 8,622,584 , the U.S. Patent No. 8,425,071 , the U.S. Patent No. 9,028,087 and the U.S. Patent Publication No. 2015/0253488 each incorporated herein by reference. Finally shows 8E a canopy lighting in the U.S. Patent No. 9,182,096 and incorporated herein by reference. The light-emitting devices described herein may also be used in various other luminaires, such as those disclosed in U.S. Pat U.S. Patent Publication No. 2014/0347885 disclosed waveguide - based trimmings in US Pat U.S. Patent Publication No. 2012/0051041 disclosed Troffer-like lights and / or in the in the U.S. Patent Publication No. 2014/0355302 disclosed waveguide-based garage lights, each incorporated herein by reference. Other and similar lights can be implemented using the circuit described above.

As is known to those skilled in the art, lamps have been developed using solid state light sources, such as LEDs, in conjunction with a conversion material separate from or remotely located from the LEDs. Such arrangements are in the U.S. Patent No. 6,350,041 entitled "High Output Radial Dispersing Lamp Using a Solid State Light Source," which is incorporated herein by reference. Suitable lamps may include a solid state light source that transmits light through a separator or manifold having one or more phosphors and / or stabilized quantum dot structures. The manifold may distribute the light in a desired pattern and / or change its color by converting at least a portion of the light through the phosphor (s), quantum dot structures and / or other conversion material to a different wavelength. In some embodiments, the separator separates the light source a sufficient distance from the manifold so that heat from the light source is not transmitted to the manifold when the light source carries increased currents required for the room lighting. Additional far-flare technologies are in the U.S. Patent No. 7,614,759 entitled "Lighting Device", which is incorporated herein by reference.

The present description again addresses the stabilized quantum dot structures which, as described above, can be incorporated in light emitting devices having any of a variety of housing, light and lamp configurations, such as those described above. Hereinafter, a process for producing the stabilized quantum dot structures which can have improved stability is described.

The method comprises forming a luminescent particle comprising one or more semiconductors and forming a buffer layer on the luminescent particle comprising an amorphous material. This forms a coated luminescent particle. The coated luminescent particle is treated to form a stabilized quantum dot structure (or "a treated coated luminescent particle") having a quantum efficiency of at least 0.7, after being exposed to a blue light flux of about 30 W / cm ² at a temperature of 80 exposed to 85 ° C and a relative humidity of 5% for 500 hours. Additionally or alternatively, the stabilized quantum dot structure may have a quantum efficiency of at least about 0.6 when exposed to a blue light flux of about 30 W / cm ² at a temperature of 80 to 85 ° C and 85% relative humidity for 500 hours , As described below, the treatment may be a pH treatment or a heat treatment.

According to another embodiment, a method for producing a stabilized quantum dot structure comprises forming a luminescent particle comprising one or more semiconductors, and forming a buffer layer comprising an amorphous material on the luminescent particle to thereby form a coated luminescent particle , A barrier layer containing oxygen, carbon and / or nitrogen is formed on the coated luminescent particle as described above to form a stabilized quantum dot structure having a quantum efficiency of at least about 0.7 when exposed to a blue blue light flux of about 30 W / cm ² at a temperature of 80-85 ° C in a relative humidity of 5% for 500 hours. Additionally or alternatively, the stabilized quantum dot structure may have a quantum efficiency of at least about 0.6 when exposed to a blue light flux of about 30 W / cm ² at a temperature of 80 to 85 ° C in a relative humidity of 85% for 500 hours. In some embodiments, the buffer layer may be a treated buffer layer as previously described elsewhere in this specification.

Treating the buffer layer to form a treated coated luminescent particle may include heating (annealing) the coated luminescent particle to an elevated temperature, for example, at about 100 ° C to about 800 ° C. Annealing may be followed by cleaning and drying of the coated luminescent particle, which cleaning may include washing to remove unwanted by-products and / or "dust" removal. Typically, annealing is conducted at a temperature in the range of about 400 ° C to about 800 ° C. A suitable annealing environment may be nitrogen, an inert gas, dry air, or other atmosphere (eg, ambient air or a reactive gas such as hydrogen, forming gas, oxygen, fluorinated gas, etc.). Typically, annealing is performed for a period of about 5 minutes to about 120 minutes. In one example, the coated luminescent particle is heated in nitrogen at 500 ° C for 5 minutes. After annealing, the luminescent particle is cooled to room temperature. It is believed that annealing the coated luminescent particle promotes densification of the buffer layer, which in turn may lead to a reduction in the atmospheric species (e.g., H ₂ O, O ₂ ) that permeates the buffer layer and the underlying semiconductor (s) can / can achieve. Thus, the stabilized quantum dot structure may have a reduced decay during LED operation. Hereinafter, a description will be given of a possible compression mechanism in the case of a silicon dioxide buffer layer.

One effect of the annealing process described above may be a transient quenching of the emission from the treated coated luminescent particle, as shown in FIG 9A which represents a quantum yield as a function of time (hours). The emission can be restored after the structure has been exposed to a blue light stream during operation (for example, after the introduction of the treated coated luminescent particles into a housing for use). Alternatively, a "pre-bake" method developed in the present work may be used so that the quantum dot structures exhibit stable emission immediately upon use. It is believed that the quenching and restoring of the emission is due to an electronic effect involving the charging and discharging of the quantum dots. The pre-bake process may include exposure of the treated coated luminescent particles to blue light in an environment of oxygen, such as air or water. For example, the treated coated luminescent particles after annealing: (a) are dispersed in water or an aqueous solution; (b) exposed to blue light for 24 hours; and (c) removed from the water / aqueous solution and dried to a powder. 9B Fig. 14 shows that after the pre-bake process, followed by housing to form an LED component / light-emitting device, the stabilized quantum dot patterns from the start of operation (time t = 0) of the light-emitting device to stable performance. The packaging may include methods known in the art as described above.

As an alternative or in addition to the annealing, the treatment of the buffer layer may comprise exposing the coated luminescent particle to a treatment solution comprising a predetermined pH. The predetermined pH of the treatment solution may range from about 6.5 to about 14, with a pH of about 10 to 12 being typical. The treating solution may be formed by adding an acidic aqueous solution and / or a basic aqueous solution to a suspension containing the coated quantum dot structure to reach the predetermined pH. The acidic aqueous solution may comprise an acid selected from the group consisting of: HCl, HBr, H ₃ PO _4, and H ₂ SO ₄ , and the basic aqueous solution may be a base selected from the group consisting of NaOH, KOH, NH ₄ OH and H ₂ SO ₄ include. The treating solution may be heated to a temperature in the range of about 40 ° C to about 100 ° C during the exposure of the coated luminescent particle (s). The suspension with the coated luminescent particle (s) can be formed as described below.

In some embodiments, after the treatment of the coated luminescent particle to form the stabilized quantum dot structure, a barrier layer containing oxygen, carbon, and / or nitrogen may be formed on the treated buffer layer. As described above, the barrier layer can be formed on the treated buffer layer or on an untreated buffer layer. In either case, the formation of the barrier layer can result in a solution phase reaction or a vapor phase reaction.

The solution phase reaction may comprise exposing the coated luminescent particle or stabilized quantum dot structure (for example, after treatment of the coated luminescent particle) to a first solution comprising at least one oxide, carbide or nitride precursor ("the precursor substance (s)"). The exposure may be at room temperature or at an elevated temperature of about 25 ° C to about 300 ° C. The precursor substance (s) may comprise a metal salt, such as a metal nitrate, metal acetate or metal chloride. The first solution is typically an aqueous solution and the precursor substance is typically contained at a concentration of 10 to 500 mg / ml, with 50 to 150 mg / ml (for example, 100 mg / ml) being typical. When an aqueous solution is used, the coated luminescent particle may have a polar surface. When the metal oxide coating is formed in a nonpolar medium, such as an organic solution, the coated luminescent particle may have a nonpolar surface (for example, by intentionally applying a hydrophobic coating). It should be noted that the term "metal oxide" is sometimes used in the present invention as an alternative to "oxide" and should not be construed as limiting the meaning of "oxide". For example, the two terms "metal oxide" and "oxide" may be used with respect to silicon dioxide (SiO _x ), although silicon (Si) is a semiconductor rather than metal. Exposure to the precursor substance (s) may include injecting or pouring the first solution comprising the precursor substance (s) into a heated suspension of coated luminescent particles, or injecting or pouring a suspension of coated luminescent particles into the first Include solution at an elevated temperature. Alternatively, the coated luminescent particles may be mixed into the first solution and sealed in a reactor, followed by a gradual increase in temperature to the elevated temperature. When the precursor substance (s) decompose, the corresponding oxygen, carbon and / or nitrogen-containing compound (for example, an oxide, carbide or nitride) is added to the surface of the coated luminescent particle in the form of a coating to thereby form the barrier layer.

The formation of the barrier layer may further comprise exposing the coated luminescent particle to a second solution comprising an additive such as an acid, a base or a buffer, or a surfactant. For example, the second solution may be an aqueous solution and the additive may be a base such as potassium hydroxide, sodium hydroxide or ammonium hydroxide in a concentration of 0.1-10M. Exposure of the coated luminescent particle of the first solution comprising the precursor substance (s) and the second solution comprising the additive or surfactant may occur simultaneously. The additive or surfactant may help to control the pH of the mixture or the To control surface properties of the luminescent particle and / or the barrier layer. Exposure to the first and optionally the second barrier-forming solution may occur over a period of time, such as between 10 minutes and 16 hours, with 30 minutes to 2 hours (for example, 1 hour) being typical.

The vapor phase reaction to form the barrier layer may include a vapor deposition process known in the art, such as atomic layer deposition (ALD) or chemical vapor deposition (CVD). In ALD, the barrier layer is grown on the buffer layer or on the treated buffer layer by exposure to alternating gaseous precursor substances (eg, a metal volumizer and an oxygen precursor). In contrast, in vapor deposition, the gaseous precursors are typically not coexistent in the reactor, but instead are introduced separately in a series of sequential pulses. The presence of the buffer layer comprising an amorphous material on the surface of the luminescent particle serves to prevent deterioration of the underlying semiconductor layer (s) during vapor deposition.

In the case of a buffer layer comprising silicon dioxide (SiO _x , where 0.5 ≤ x ≤ 2.5, for example, SiO ₂ ), the above-described annealing treatment for stabilization may be used to condense Si-OH groups to Si-O-Si Groups according to the following reaction: Si-OH + Si-OH → Si-O-Si + H ₂ O. Consequently, the silica composite can be rearranged and the buffer layer densified. Due to these structural and chemical changes during annealing, the buffer layer may have an increased number of Si-O-Si bonds as compared with the Si-OH bonds after annealing. This can be verified experimentally using Fourier Transform Infrared Spectroscopy (FTIR) data, as the vibrational spectra of silica during heat treatment may show predictable changes.

Referring to 10 For example, the FTIR spectra obtained from the silica-coated luminescent particles may include one or more intensity peaks (spectroscopic signals) that may be associated with the Si-O-Si composite, and one or more intensity peaks (spectroscopic signals) representing the Si-OH (silanol) groups can be assigned. As the heating progresses, the spectroscopic signals associated with the non-densified silanol groups are reduced relative to the signals associated with the densified Si-O-Si composite. As such, the vibrational spectrum of a given sample of silica-coated luminescent particles can be used to measure the density of the silica buffer layer and provide a semiquantitative measure of the concentration of non-densified silanol groups.

For example, after annealing to form an increased density, one or more of the following three distinct changes in the FTIR spectra can be observed: (a) the intensity of the silanol (SiO-H) signal is approximately 3300 cm ^-1 Reduced composite (Si-O-Si) signal at about 1050 cm ^-1 ; (b) the silanol (Si-OH) peak at about 950 cm ^-1 is converted from a discrete peak to a shoulder with no observable peak; and (c) the intensity of the silanol (Si-OH) peak at about 950 cm ^-1 is reduced at about 1050 cm ^-1 with respect to the composite (Si-O-Si) signal. Accordingly, an FTIR spectrum obtained from the silica-coated luminescent particles annealed for stabilization may have a peak intensity ratio (R) of at least about 35, where R is the intensity at about 1050 cm ^-1 (I ₁₀₅₀ corresponding to Si Corresponds to the intensity at about 3300 cm ^-1 (I ₃₃₀₀ , which corresponds to the non-compressed silanol groups). In other words, R = I ₁₀₅₀ / I ₃₃₀₀ ≥ 35. In some cases, as shown in the examples below, R may be at least about 40, at least about 45, or at least about 50, and R may also be as high as 75 or as high as 65.

In addition to the increased density, further changes that may occur in the buffer layer during annealing of a coated luminescent particle include a reduction in mass and / or a reduction in thickness, as more fully described in the examples.

Examples

A luminescent particle having a core-shell structure (either a core / first-shell structure (e.g., CdSe / CdS) or a core / first-shell / second-shell structure (e.g., CdSe / CdS / ZnS) as before described) can be prepared using methods known in the art or purchased commercially from a vendor.

Formation of the buffer layer

The buffer layer comprising the amorphous material may be formed by an inverse micellar condensation reaction using a suitable precursor on the luminescent particle. When the amorphous material comprises amorphous silica, the precursor substance may comprise tetraethyl orthosilicate (TEOS) as described in this example.

First, a mixture of heptane, water and a surfactant such as Brij ^® L4 is prepared. The heptane, the surfactant and the water can be combined in volume ratios of about 10: 5: 1. The surfactant forms micelles of a controlled size that surround the water (the aqueous or hydrophilic phase) and the heptane (the hydrophobic phase) remains outside of the micelles. The luminescent particles, such as the CdSe / CdS core-shell particles, are added to the mixture. Typically, the luminescent particles at a concentration of 0.2-2 nmol per milliliter (0.2-2 nmol / ml) are added to the solution. In addition, a base (for example, 28 to 30 wt .-% ammonia solution) with a volume ratio of base to water of 1: 8 are added. The resulting mixture can be stirred for 10 to 20 minutes, and then the TEOS can be added. Adding the TEOS can be done all at once or in small amounts over a period of hours or days. The thickness of the silicon dioxide coating (the "buffer layer" described above) on the luminescent particle can be controlled by the amount of TEOS added to the mixture.

A likely mechanism of silica growth on the luminescent particle involves the exchange of ligands in the mixture and the transfer of the luminescent particle from the hydrophobic phase to the hydrophilic phase, where growth of the silica may occur.

pH treatment of the buffer layer

After cleaning, a powder with coated luminescent particles comprising CdSe / CdS / SiO _x (which can be prepared as described above) is dispersed in a basic aqueous (alkaline) solution. Several bases may be used to prepare the alkaline solution, including, but not limited to, potassium hydroxide, sodium hydroxide or ammonium hydroxide. The concentration of the base in the solution is typically between 0.01 M and 1.0 M, with the higher concentrations facilitating the distribution of the coated particles but possibly etching the SiO _x shell to a greater extent. The suspensions with the coated particles can be prepared at concentrations <50 mg / ml, with 10 mg / ml being typical. Usually, but not always, sonication is used to obtain a homogeneous suspension. In some cases, the sonication may be carried out for up to several hours.

The suspension containing the coated particles is diluted with deionized water to a concentration of <5 mg / ml, with 2 mg / ml being typical. The concentration of the coated particles is preferably kept relatively low to prevent aggregation and flocculation. To this solution is optionally added tribasic sodium citrate in a concentration of 0.5 to 10 mg / ml.

The pH can then be adjusted to a desired initial value by adding an acidic aqueous solution (for example, HCl, HBr, H ₃ PO ₄ , H ₂ SO ₄ ) to reduce the pH or a basic aqueous solution (for example NaOH, KOH, NH ₄ OH, H ₂ SO ₄ ) is added to increase the pH. The initial pH may range between 6.5 to 14, with a value of about 11 being typical. In addition, a pH buffer can be added at this stage to better control the pH.

A PTFE-coated magnetic stir bar can be added and the reaction vessel sealed (for example, with a rubber septum). The sealed container may be placed in an oil bath at the desired reaction temperature, typically between 40 ° C and 100 ° C, although the reaction may also be carried out at room temperature. The reaction vessel may then be thermally equilibrated for typically a period of about 30 minutes.

6A - 6B show the quantum yield for the stabilized luminescent particles coated with a treated layer comprising amorphous silica and an ionic species (K) due to the pH treatment. It can be seen that improved stability can be achieved for higher pH treatments.

The presence of an additional chemical species in the treated layer can be verified by EDX, and the relative intensity of the additional chemical species can be used to determine the qualitative relative amount of the additional chemical species in the buffer layer as described above.

Annealing the buffer layer

A powder having coated luminescent particles comprising CdSe / CdS / SiO _x which can be prepared as described above is subjected to an annealing treatment to densify the buffer layer (SiO _x ). The powder is heated for 5 min in a nitrogen atmosphere at 500 ° C and then cooled to room temperature. 11 Figure 12 shows the quantum yield as a function of time (hours) for the exemplary coated luminescent particles with and without annealing and a tremendous increase in stability due to the annealing treatment.

The densification of the buffer layer as a result of annealing is demonstrated by mass loss data obtained for the coated luminescent particles. Referring to 12 showing the weight (%) as a function of temperature (° C), three curves are shown corresponding to first, second and third annealing steps of the coated luminescent particles. The mass loss observed for each of the three curves below 200 ° C is attributed to water vapor and / or other adsorbed atmospheric components. Above 200 ° C, during the first annealing step, a fairly substantial mass loss (nearly 4%) occurs which is not observed during the second or third annealing step. It is believed that this mass loss is due to the condensation of the Si-OH groups and the rearrangement of the silica composite, which leads to a higher proportion of Si-O-Si groups after annealing than before.

Further evidence of compaction during annealing can be observed by TEM studies of the coated luminescent particles. 13A - 13D show TEM images of the coated luminescent particles after the annealing treatment. 14 shows a diagram of the particle size distribution before and after annealing, which is determined from the analysis of the TEM images. Before annealing, an average particle diameter of 23.4 nm is measured; after annealing, the average particle diameter drops to 21.2. In this example, this corresponds to a volume reduction of approx. 20%. In general, a volume reduction of 5-25% is observed after annealing. The TEM images show no change in the size of the semiconductor quantum dot underlying the silicon dioxide coating or shell, and thus the TEM data suggests that the densification is limited to the buffer layer.

Characterization of the buffer layer

Unstabilized and stabilized (by annealing) quantum dot structures using FTIR analysis are examined to determine the properties of densified buffer layers.

The FTIR spectra are recorded using an FTIR spectrometer operating in ATR mode. Untreated and tempered coated luminescent particles in the form of powder samples are placed directly on the diamond ATR crystal and densified with an anvil prior to measurement. The spectra are background corrected, converted to absorbance units and normalized to the highest peak before determining intensity ratios. If there is no peak / peak, as is the case for the silanol-Si-OH signal for the treated stable samples, the shoulder position is used instead. The peak assignments in this study are common for silicate materials as described in Brinker, CJ Scherer, GW, "Sol-Gel Science: The Physics and Chemistry of Sol-Gel Processing", Academic Press Inc., 1990, pp. 541-546 described. An exemplary FTIR spectrum is in 10 shown.

To develop quantitative criteria, four sample pairs are measured before and after tempering and their spectra are analyzed for significant differences. Thus, three criteria are established to determine quantum dot structures having a densified silica buffer layer, supported by the data shown in Tables 1-3 below. It is believed that the samples of the coated luminescent particles satisfying one or more (or all) of these criteria were subjected to an annealing treatment as described above to densify the buffer layer to produce a stabilized quantum dot structure.

As can be seen first from Table 1, the first criterion is that the ratio (R = I1050 / I3300) of the peak intensity between the composite (Si-O-Si) signal at about 1050 cm ^-1 and the silanol SiO-H Signal at about 3200-3400 cm ^-1 (for example 3300 cm ^-1 ) is at least about 35. As previously mentioned, R may also have at least about 40, at least about 45, or at least about 50, and in some cases even a high, value of 75 or a high value of 65. Table 1: peak intensity ratios (R = I ₁₀₅₀ / I ₃₃₀₀ ) for untreated and treated quantum dot structures sample pair Ratio R - untreated, unstable quantum dot structures Ratio R - treated, stable quantum dot structures 1 21.5 41.3 2 26.0 38.8 3 27.5 61.6 4 15.5 54.4

Referring to Table 2, the second criterion is that the FTIR spectrum does not have a pronounced silanol (Si-OH) intensity peak at about 950 cm ^-1 . Table 2: Structure at 950 cm ^-1 sample pair Structure - untreated, unstable Structure - treated, stable 1 discrete tip no discrete tip 2 discrete tip no discrete tip 3 discrete tip no discrete tip 4 discrete tip no discrete tip

Referring to Table 3, the third criterion is that the ratio (R * = I ₁₀₅₀ / I ₉₅₀ ) of the peak intensity between the composite (Si-O-Si) signal at about 1050 cm ^-1 and the silanol (Si) OH) signal at about 950 cm ^{-1 is} at least about 2.8. The ratio R * may also be at least about 3.0, at least about 3.2, or at least about 3.4, with typically the ratio R * not greater than about 6, or not greater than about 5. Table 3: Peak intensity ratios (R * = I ₁₀₅₀ / I ₉₅₀ ) for untreated and treated quantum dot structures sample pair Ratio R * - untreated, unstable Ratio R * - treated, stable 1 2.2 3.2 2 2.6 2.9 3 2.6 4.3 4 1.9 3.4

Formation of the barrier layer

Solution phase reaction. In this example, a zinc oxide barrier layer is formed on the coated particles as described above using a solution phase reaction. An aqueous solution of a zinc precursor substance (for example, Zn (NO ₃ ) ₂ , Zn (OAc) ₂ , ZnCl ₂ ) is prepared at a concentration of 10 to 500 mg / ml, with 100 mg / ml being typical. A separate aqueous solution of a base is also prepared using, for example, potassium hydroxide, sodium hydroxide or ammonium hydroxide at a concentration of 0.1 to 10.0M. The zinc solution and the base solution are loaded into separate syringes and injected into the reaction vessel for a period of time, between 10 minutes to 16 hours, with 1 hour being typical.

After the injection is completed, the reaction mixture is cooled to room temperature and purified / separated by centrifugation, depositing CdSe / CdS / SiO ₂ / ZnO as a solid orange residue. The clear, colorless supernatant is poured off. The solids are then washed twice with deionized H ₂ O and once with methanol. The purified solids are suspended in minimal methanol, transferred to a vial and dried in vacuo to dry powder.

The TEM micrographs in 16A and 16B For example, the quantum dot structures before (A) and after (B) show the addition of zinc oxide through the solution phase coating process.

Vapor-phase reaction. In this example, zinc oxide and aluminum oxide barrier layers, as described above, are formed on the coated particles using ALD. Doses of a metal precursor substance (typically diethylzinc or trimethylaluminum) and an oxygen precursor substance (water or oxygen) are alternately added at dosing times of 0.1 to 10 s (typically 1 s), followed by a pumping cycle (to <100 mtorr) or rinsing after each metal - or oxygen cycle of non-reactive gas (argon or nitrogen) for 0.1-300 s (typically 60 s). The process is carried out at room temperature to 300 ° C (typically 150 ° C) for 5-500 cycles at pressures of about 1 Torr. Typically, the material is moved after 20 cycles (eg, by mechanical grinding or moving the material) to completely cover all sides of each QD. The TEM images of the coated particles are in 17A - 17C (CdSe / CdS / SiO _x / Al ₂ O ₃ ) and 18A - 18C (CdSe / CdS / SiOx / ZnO). The same ALD conditions previously described as typical conditions were used to prepare the Al ₂ O ₃ and ZnO barrier layers on the luminescent particles comprising CdSe / CdS / ZnS, as shown in FIG 19A - 19C and 20A - 20C shown. The results show that the silica buffer layer enables the growth of a metal oxide barrier layer and prevents the semiconductor material from decaying during ALD.

Although the present invention has been described in detail with respect to particular embodiments, other embodiments are possible without departing from the present invention. Thus, the spirit and scope of the appended claims should not be limited to the description of the preferred embodiments contained herein. All embodiments which literally or equivalently fall within the meaning of the claims are intended to be embraced therein.

Furthermore, the advantages described above are not necessarily the only advantages of the present invention, and it is not necessarily to be expected that all the advantages described will be obtained with each embodiment of the invention.

Claims (35)

A stabilized quantum dot structure for use in a light-emitting device, wherein the stabilized quantum dot structure comprises: a luminescent particle comprising one or more semiconductors; a buffer layer over the luminescent particle, the buffer layer comprising an amorphous material; and a barrier layer over the buffer layer, wherein the barrier layer comprises oxygen, nitrogen and / or carbon. The stabilized quantum dot structure of claim 1, wherein the amorphous material is selected from the group consisting of amorphous silica, amorphous titania, amorphous carbon, amorphous alumina, amorphous silicon oxycarbide or an amorphous aluminosilicate. A stabilized quantum dot structure according to claim 1 or 2, wherein the barrier layer comprises an oxide, a carbide, a nitride, an oxynitride or an oxycarbide. The stabilized quantum dot structure of claim 3, wherein the barrier layer comprises an insulating oxide selected from the group consisting of alumina, zirconia and hafnia. The stabilized quantum dot structure of claim 3, wherein the barrier layer is a semiconducting oxide selected from the group consisting of zinc oxide, titanium dioxide, indium oxide, tin oxide, nickel oxide and copper oxide; or a conductive oxide selected from the group consisting of indium-tin oxide, aluminum-doped zinc oxide and gallium-doped zinc oxide. The stabilized quantum dot structure of claim 3, wherein the barrier layer comprises: a nitride selected from the group consisting of silicon nitride, aluminum nitride, boron nitride and gallium nitride; or a carbide selected from the group consisting of silicon carbide and boron carbide. A stabilized quantum dot structure according to any one of claims 1 to 6, wherein the buffer layer and / or the visible light blocking layer are substantially transparent. The stabilized quantum dot structure of any one of claims 1 to 7, wherein the buffer layer further comprises an ion species selected from the group consisting of K and Na, wherein the buffer layer is a treated buffer layer. A stabilized quantum dot structure according to any one of claims 1 to 8, wherein the buffer layer is a densified buffer layer comprising amorphous silica, wherein an FTIR spectrum of the stabilized quantum dot structure has a peak intensity ratio R = I ₁₀₅₀ / I ₃₃₀₀ of at least about 35, where I ₁₀₅₀ a Peak intensity at about 1050 cm ^-1 and I _{3300 is} a peak intensity at about 3300 cm ^-1 . The stabilized quantum dot structure of any one of claims 1 to 9, wherein the luminescent particle comprises a core-shell structure comprising a semiconductor core and one or more semiconductor shells overlying the semiconductor core. A stabilized quantum dot structure according to any one of claims 1 to 10, wherein both the buffer layer and the barrier layer have a thickness of about 2 nm to about 50 nm. The stabilized quantum dot structure according to any one of claims 1 to 11, wherein the luminescent particle has a size of about 100 nm or less. A stabilized quantum dot structure according to any one of claims 1 to 12, having a quantum efficiency of at least about 0.7 when exposed to a blue light flux of 30 W / cm ² at a temperature of 80 to 85 ° C and a relative humidity of 5% for 500 hours is exposed. A light-emitting device comprising a diode chip (LED chip) emitting blue light having a dominant wavelength of 425 nm to 475 nm in optical communication with a plurality of the stabilized quantum dot structures according to any one of claims 1 to 13 for down-converting light, emitted from the blue LED chip. A stabilized quantum dot structure for use in a light-emitting device, wherein the stabilized quantum dot structure comprises: a luminescent particle comprising one or more semiconductors; a buffer layer over the luminescent particle, wherein the buffer layer comprises an amorphous material and an additional chemical species for stabilizing the quantum dot structure. The stabilized quantum dot structure of claim 15, wherein the additional chemical species comprises an ion species selected from the group consisting of K and Na. The stabilized quantum dot structure of claim 15 or 16, further comprising a barrier layer over the buffer layer, wherein the barrier layer comprises oxygen, nitrogen and / or carbon. The stabilized quantum dot structure of any one of claims 15-17, wherein the luminescent particle comprises a core-shell structure comprising a semiconductor core and one or more semiconductor shells overlying the semiconductor core. A stabilized quantum dot structure according to any of claims 15 to 18, having a quantum efficiency of at least about 0.7 when exposed to a blue light flux of about 30 W / cm ² at a temperature of 80 to 85 ° C and a relative humidity of 5% for 500 Hours is suspended. A light-emitting device comprising a diode chip (LED chip) emitting blue light having a dominant wavelength of 425 nm to 475 nm in optical communication with a plurality of the stabilized quantum dot structures according to any one of claims 15 to 19 for down-converting light emitted from the blue LED chip. A stabilized quantum dot structure for use in a light-emitting device, wherein the stabilized quantum dot structure comprises: a luminescent particle comprising one or more semiconductors; a treated buffer layer comprising amorphous silica over the luminescent particle; wherein the stabilized quantum dot structure has a quantum efficiency of at least about 0.7 when exposed to a blue light flux of about 30 W / cm ² at a temperature of 80 to 85 ° C and a relative humidity of 5% for 500 hours. The stabilized quantum dot structure of claim 21, wherein the treated buffer layer is a densified buffer layer, wherein an FTIR spectrum of the stabilized quantum dot structure has a peak intensity ratio R = I ₁₀₅₀ / I ₃₃₀₀ of at least about 35, where I _{1050 has} a peak intensity at about 1050 cm ^-1 and I _{3300 is} a peak intensity at about 3300 cm ^-1 . The stabilized quantum dot structure of claim 21 or 22, wherein the treated buffer layer further comprises an ion species selected from the group consisting of K and Na. A light-emitting device comprising a diode chip (LED chip) emitting blue light having a dominant wavelength of 425 nm to 475 nm in optical communication with a plurality of the stabilized quantum dot structures according to any one of claims 21 to 23, for downconverting light, which is emitted from the blue LED chip, the stabilized quantum dot structures having a quantum efficiency of at least about 0.7 at time t = 0 during operation of the light-emitting device. A method of making a stabilized quantum dot structure, the method comprising: Forming a luminescent particle comprising one or more semiconductors; Forming a buffer layer comprising an amorphous material on the luminescent particle thereby to form a coated luminescent particle; and Forming a barrier layer comprising oxygen, nitrogen and / or carbon on the coated luminescent particle to improve its stability, thereby forming a stabilized quantum dot structure. The method of claim 25, wherein forming the barrier layer comprises a solution phase reaction or a vapor phase reaction. The method of claim 25 or 26, further comprising, prior to forming the barrier layer, treating the coated luminescent particle for improved stability, the treatment includes: Exposing the coated luminescent particle to a treatment solution having a pH of about 6.5 to about 14, or Annealing the coated luminescent particle, thereby densifying the buffer layer. A method of producing a stabilized quantum dot structure, the method comprising: forming a luminescent particle comprising one or more semiconductors; Forming a buffer layer comprising an amorphous material on the luminescent particle thereby to form a coated luminescent particle; and treating the coated luminescent particle to improve its stability and form a stabilized quantum dot structure, wherein the stabilized quantum dot structure has a quantum efficiency of at least about 0.7 when exposed to a blue light flux of about 30 W / cm ² at a temperature of 80 to 85 ° C and a relative humidity of 5% for 500 hours. The method of claim 28, wherein the treatment comprises the step of exposing the coated luminescent particle to a treatment solution having a pH of from about 6.5 to about 14. The method of claim 28 or 29, further comprising, after treatment, forming a barrier layer comprising oxygen, nitrogen and / or carbon on the coated luminescent particle. The method of any one of claims 28 to 30, wherein the treatment comprises annealing the coated luminescent particle, thereby densifying the buffer layer. The method of claim 31, wherein the annealing is performed at a temperature in the range of about 400 ° C to 800 ° C. The method of claim 31 or 32, wherein the treatment further comprises, after tempering, a step of exposing the coated luminescent particle to blue light in an oxygen-containing environment. The method of claim 33, wherein the environment comprises air or water. The method of any one of claims 28 to 34, wherein the treatment is performed prior to incorporation of the stabilized quantum dot structure.

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